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post #1 of (permalink) Old 02-12-2004, 03:30 PM Thread Starter
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Hei OR Tfi?

I have looked around and searched. They both seem like viable upgrades, but the HEI seems simpler,,,, Which do you guys recomend for a 79 cj5 6 cyl??
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post #2 of (permalink) Old 02-12-2004, 04:00 PM
 
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Re: Hei OR Tfi?

I think they are both excellant upgrades. I'd base it on what was most readily available to me. If you can find a TFI coil and bracket lying around, the TFI upgrade is probably the cheapest. Then all you need is the adapter, cap and rotor. For the HEI, you will need the distributor, a new drive gear, and to replace at a minimum the cap and rotor. The TFI, you can buy it all off the shelf of your auto parts store, for the HEI, you could buy a distributor, but most likely chose to junkyard scrounge.

Flip a coin. I have the HEI, and like the unitized system and clean hookup of a single wire. If you plan to go fuel injection, I can tell you the HEI system is very compatible with a GM based throttle body system like Howell, or the Megasquirt.

The best argument for Teamrush's TFI system is the wide spacing of the terminals on the distributor cap, and the fact you retain your factory ignition curve (both mechanical and vacuum).
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post #3 of (permalink) Old 02-12-2004, 07:50 PM
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Re: Hei OR Tfi?

</font><blockquote><font class="small">In reply to:</font><hr />
For the HEI, you will need the distributor, a new drive gear, and to replace at a minimum the cap and rotor.

[/ QUOTE ]

Actually, there is another write up on just using the HEI module with the duraspark distributor. That would be my choice to do. Then use the ford coil.
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post #4 of (permalink) Old 02-12-2004, 08:17 PM
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Re: Hei OR Tfi?

I used the HEI mod with a Motorcraft distributor. Mine is a 75, so I didn't need to remove the resistor wire from the circuit, so it was extremely easy.

If I had a 6cyl, I would go with the HEI distributor. I have a friend that did this and the difference was night and day. I believe the one you need to find is one from a GM 250 6cyl engine. You then remove the GM drive gear and replace it with the AMC drive gear off your existing distributor. This is all from memory and I have never done it myself, so do a search to get the real specifics.
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post #5 of (permalink) Old 02-12-2004, 09:12 PM
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Re: Hei OR Tfi?

I ended up doing the TFI upgrade on my 84. It was easy to obtain all of the parts, with the exception of the coil bracket. I found a bracket on an 80's taurus that I used to mount the coil to the fender. I do not like all of the wiring and would like to eliminate/replace/or move my stock ignition module, but just have not gotten that far in the last 2 years. Overall, I have been pleased, and it was easy.

The link that Will posted looks interesting. How would the HEI module compare to the stock module to an MSD module? -- Mike
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post #6 of (permalink) Old 02-13-2004, 06:04 AM
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Re: Hei OR Tfi?

I did the GM HEI. It does make a night and day difference and is oh so simple to install. I understand the advantages of the TFI system, but I've also read numerous posts from people trying to trouble shoot them. I've got just about $100.00 into my HEI. Just a note.. the caps for them are about 20-25 bucks. Also I noticed someone recently started selling them on e-bay with the AMC gear already installed for about $100.00. I don't think they rebuild or refurbish them in any other way though. [img]images/graemlins/grin.gif[/img]
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post #7 of (permalink) Old 02-13-2004, 06:46 AM
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Re: Hei OR Tfi?

""How would the HEI module compare to the stock module to an MSD module? ""

Both modules are designed to turn on and off, making them the same in that respect.

The difference is the GM coil and the TFI coils have a lower primary resistance, and are built to handle, and use, a full 12 volts instead of having the voltage dropped with an ignition resistor. Without the full 12 volts it acts like a stock coil - no benefit.

The stock Jeep module (a Ford DuraSpark I) cannot handle the increased current of those coils for long. It overheats and frys. Granted, they may work for awhile, but eventually they ---.

The module originally used with the TFI coil (the module's called a Thick Film Ignition module - thus TFI) is not easily adapted to the Jeep engines - you have to swap the entire distributor.

The HEI module, as well as the TFI's module, are designed to handle that extra current.

The extra current is used to create higher voltage and higher current in the coil secondary - thus the term HEI - High Energy Ignition.
The real result is the spark duration across the plug - the spark is there for much longer time - 2.5 milliseconds vs. .75 milliseconds. The longer duration spark ignites more mixture - thus increasing power and lowering emissions - since it burns more.
The HEI also has a side benefit - the rise time of the spark is about 4 times faster - hitting the cylinder better - kinda like an impact wrench hitting a stuck bolt.

The larger cap on either the Ford upgrade distributor or HEI spaces the terminals farther apart, so it has the ability to handle increased secondary voltages.

The MSD - Multiple Spark Discharge - is an entirely different ignition system. It is a true CD ignition rather than a Kettering ignition. It has an even faster rise time, and it fires several times for each firing stroke. But the spark duration is very short, on the order of .2 milliseconds. That makes up for the lack of duration by firing several times. Unfortunately it stops doing it's multiple firing around 3000 RPM.
The end result is the MSD and the GM HEI run about the same in a Jeep. But either are definate improvements over the stock ignition - a very noticable improvement.
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post #8 of (permalink) Old 02-13-2004, 08:44 AM
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Re: Hei OR Tfi?

A couple days ago, I had all the spark plug wires off and drapped over the engine and fenders to do a compression test. Two of the wires that I could see were a little above the driver's side fender. The spark plug connector is about an inch inside the boot and the boot was about a 1/2" above the painted fender. When I cranked the engine, the MSD had no problem bridging that 1-1/2" gap and creating a BIG spark. I promptly unhooked the MSD for the rest of the cylinders but by no means would I want to pull a spark plug wire off while the engine is running to find a missing cylinder.
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post #9 of (permalink) Old 02-13-2004, 11:04 AM
 
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Re: Hei OR Tfi?

[quoteThe MSD - Multiple Spark Discharge - is an entirely different ignition system. It is a true CD ignition rather than a Kettering ignition. It has an even faster rise time, and it fires several times for each firing stroke. But the spark duration is very short, on the order of .2 milliseconds. That makes up for the lack of duration by firing several times. Unfortunately it stops doing it's multiple firing around 3000 RPM.
The end result is the MSD and the GM HEI run about the same in a Jeep. But either are definate improvements over the stock ignition - a very noticable improvement]

[/ QUOTE ]

So does this mean that the GM HEI doesn't run well above 3000 RPM's?
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post #10 of (permalink) Old 02-13-2004, 01:28 PM
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Re: Hei OR Tfi?

1. The only time I got an apology outta TR...
2. Have you read This thread,
3. Or This one?
4. These have some good information....
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